Process For Making A Catalytic Electrode And Electrochemical Cell Using The Electrode

ABSTRACT

A process for making a catalytic electrode, a process for making an electrochemical cell with a catalytic electrode, and an electrochemical cell made according to the process. The catalytic electrode has an active layer comprising a catalytic material, an electrically conductive material and a binder, and a gas diffusion layer including a material that is permeable to gas entering or escaping from the cell but essentially impermeable to electrolyte. The gas diffusion layer is adhered to the active layer by a patterned pressure bonding process to provide the catalytic electrode in which the entire gas diffusion area is adhered to the active layer, with areas of relatively high and relatively low adhesion. The electrode has a high overall bond strength, and the permeability of the gas diffusion layer remains high it has been adhered to the active layer to provide excellent high power capability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/877,251, filed Dec. 27, 2006.

BACKGROUND

This invention relates to a catalytic electrode, particularly anelectrode with a nano-catalytic material, an electrochemical cellcontaining the catalytic electrode, and processes for making thecatalytic electrode and the electrochemical cell.

There is a wide variety of electrochemical cells that have catalyticelectrodes. Examples include, but are not limited to, fuel cells,metal-air battery cells, gas (e.g., hydrogen) generating cells, andelectrochemical sensor cells. Examples of such cells are found in U.S.Pat. Nos. 5,242,565; 5,308,711; 5,378,562; 5,567,538; 5,707,499;6,060,196; 6,461,761; 6,602,629; 6,911,278; 7,001,689 and 7,001,865; andin International Patent Publication No. WO 00/36677.

An advantage of cells with catalytic electrodes is that they can use oneor more active materials that are not contained within cell or batteryhousings, thereby providing long use time (e.g., discharge capacity)with a cell having a minimum volume. There is an ongoing desire toimprove the performance of such electrochemical cells, such as byimproving electrical characteristics (e.g., operating voltage, poweroutput, energy density, discharge capacity, charging efficiency, cyclelife and fade), storage characteristics, leakage resistance, cost,environmental impact of waste disposal, and safety in manufacturing.

One way to improve the electrical characteristics is through the use ofa catalytic material having greater catalytic activity. One approach todoing so has been to use nano-catalysts (catalyst materials withparticles smaller than one micrometer (μm) because their large surfacearea provides more reactive sites. To provide good electricalconductivity and low internal resistance within the catalytic electrodeand to provide a large reactive surface area with the electrode, thecatalytic material is often combined with a porous material withexcellent electrical conductivity. Examples of such efforts can be foundin U.S. Pat. No. 7,087,341; U.S. Patent Publication No. 2006/0226564;U.S. Patent Publication No. 2006/0269823; U.S. Patent Publication No.2007/0092784; U.S. patent application Ser. No. 11/482,290, filed Jul. 7,2006; and Unexamined Japanese Patent Publication No. 2006-252,797.

Because of the high reactivity of nano-catalyst materials, it may benecessary to process the nano-catalyst material in an inert environment,such as an Argon atmosphere. This places restrictions on and adds costto the manufacturing process that can be undesirable, especially forlarge scale, high speed manufacturing. Previous efforts to control thereactivity of nano-particulate catalyst compositions include processesin which the substrate particles (e.g., an activated carbon) andnano-catalyst particles (e.g., a nano-metal) are treated in a liquidmedium (e.g., a lower alcohol such as methanol), and the nano-particlesare oxidized by removing the liquid medium and contacting thenano-particles with an oxidant.

Previous efforts have not been completely successful in producingcatalytic electrodes and electrochemical cells using catalyticelectrodes that have improved performance characteristics and are easy,economical and safe to manufacture.

SUMMARY

Some disclosed embodiments provide a process for manufacturing acatalytic electrode and/or an electrochemical cell using the catalyticelectrode in an easy, economical and safe manner. Some embodimentseliminate the need for mixing in an inert atmosphere the components ofthe catalytic material or the resultant catalytic composition used tomake the active layer of the electrode. Some embodiments eliminate theuse of liquids that are highly volatile, flammable and/or explosive,that may pose potential health risks to workers, or that may pose a riskto the environment.

Some embodiments provide a catalytic electrode with a nano-catalystmaterial that has improved electrical properties and that will work wellin an electrochemical cell when operated at high power.

Some embodiments provide an electrochemical cell that has good leakageresistance and improved performance (e.g., greater energy density,improved discharge capacity, and higher power on discharge) than cellsmade according to the prior art and is also stable during periods ofstorage and non-use.

Disadvantages of the prior art are overcome through the use of thematerials and processes described below for mixing components of acatalytic material including nano-catalyst particles, forming acatalytic electrode from the catalytic material, and assembling theelectrode into an electrochemical cell.

Accordingly, one aspect of the invention is an electrochemical cellcomprising a catalytic electrode, a counter electrode, a separatorbetween the catalytic and counter electrodes, and an electrolyte, alldisposed within a housing having at least one opening for allowing a gasto enter into or escape from the housing; wherein: (a) the catalyticelectrode has a multilayer structure comprising an active layer and agas diffusion layer; (b) the active layer comprises a catalytic materialfor oxidizing or reducing an active material, an electrically conductivematerial, and a binder; (c) the gas diffusion layer comprises a materialthat is permeable to the gas entering or escaping the housing and isessentially impermeable to the electrolyte to seal the electrolytewithin the housing; and (d) the gas diffusion layer has a surface with agas diffusion area for diffusion of the gas therethrough, the entire gasdiffusion area is adhered to the active layer, and adhesion of the gasdiffusion area to the active layer has areas of relatively high adhesionand areas of relatively low adhesion.

Another aspect of the invention is an electrochemical cell comprising acatalytic electrode, a counter electrode, a separator between thecatalytic and counter electrodes, and an aqueous alkaline electrolyte,all disposed within a housing having at least one opening for allowingoxygen to enter the housing; wherein: (a) the catalytic electrode has amultilayer structure comprising an active layer, a gas diffusion layerand a current collector; (b) the active layer comprises a catalyticmaterial, an electrically conductive carbon and a binder; (c) the gasdiffusion layer comprises a polytetrafluoroethylene material that ispermeable to the oxygen entering the housing and is essentiallyimpermeable to the electrolyte to seal the electrolyte within thehousing; (d) the gas diffusion layer has a surface with a gas diffusionarea for diffusion of the oxygen therethrough to the active layer, theentire gas diffusion area is adhered to the active layer, and adhesionof the gas diffusion area to the active layer has areas of relativelyhigh adhesion and areas of relatively low adhesion; (e) the catalyticelectrode has sufficient permeability to be capable of providing 220mW/cm² to 700 mW/cm² maximum power on a Half Cell AC Impedance/PotentialDynamic Scan test; (f) the current collector comprises an expanded metalcomprising nickel, coated with graphite; and (g) the cell contains noadded mercury.

Yet another aspect of the invention is a process for making a catalyticelectrode for an electrochemical cell, comprising the steps: (a) mixinga catalytic material for oxidizing or reducing an active material withan electrically conductive material and a binder; (b) forming themixture from step (a) into an active layer sheet; (c) disposing a firstsurface of a gas diffusion layer sheet against a first surface of theactive layer sheet; (d) applying pressure to a second surface of theactive layer sheet and a second surface of the gas diffusion layer sheetto bond the gas diffusion layer sheet to the active layer sheet toproduce a gas diffusion area is bonded to the active layer with areas ofrelatively high adhesion and relatively low adhesion between the gasdiffusion layer and active layer; and (e) forming the bonded layers intoan electrode having adhesion between essentially the entire adjacentsecond surfaces of the bonded layers.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

Unless otherwise specified, the following definitions and methods areused herein:

-   1. Anode means the negative electrode of an electrochemical cell.-   2. Cathode means the positive electrode of an electrochemical cell.

Unless otherwise specified herein, all disclosed characteristics andranges are as determined at room temperature (20-25° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an elevational view, in cross-section, of a prismatic shapedmetal-air cell with a catalytic electrode;

FIG. 2 is an enlarged cross-sectional view through the materialconstruction of the anode casing at line 2-2 of FIG. 1, illustrating oneembodiment of the anode casing material;

FIG. 3 is an elevational view, in cross-section, of a button shapedmetal-air cell with a catalytic electrode;

FIG. 4 is a graph showing Tafel curves, with observed current on thex-axis and applied potential on the y-axis, for a zinc-air cell with anelectrode containing a conventional manganese oxide catalyst compared toa cell with an electrode containing a nano-manganese catalyst;

FIG. 5 is a graph showing power curves, with current density on thex-axis and voltage vs. zinc on the y-axis, for half cells with catalyticelectrodes containing activated carbon, one with and one without anano-manganese catalyst; and

FIG. 6 is a graph showing polarization curves, with current on thex-axis and voltage on the y-axis, for a zinc-air cell with an airelectrode containing a conventional manganese oxide catalyst compared toa cell with an electrode containing a nano-manganese catalyst.

DESCRIPTION

Electrochemical cells according to the invention can be metal-air,hydrogen generating or oxygen generating cells, for example. Theinvention is exemplified by metal-air battery cells as described below.Metal-air battery cells can be made in a variety of shapes and sizes,including button cells, cylindrical cells and prismatic cells.

Examples of prismatic and button metal-air cells are shown in FIGS. 1and 3, respectively. An embodiment of a button cell 10 including ananode casing 26 that is generally a cup-shaped metal component isillustrated in FIG. 3. Cell 10 is an air cell that includes a cathodecasing 12 that is cup-shaped, and is preferably formed of nickel-platedsteel such that it has a relatively flat central region 14 which iscontinuous with and surrounded by an upstanding wall 16 of uniformheight. Alternatively, in one embodiment the central region 14 of thecan bottom may protrude outward from the peripheral part of the canbottom. At least one hole 18 is present in the bottom of cathode can 12to act as an air entry port. The casings 12, 26 can include single ormultiple steps if desired.

An embodiment of a prismatic cell 110 including an anode casing 126 ofthe present invention is shown in FIG. 1. The cell 110 illustrated is anair cell that includes cathode casing 112, preferably formed ofnickel-plated steel. Anode casing 126 and cathode casing 112 aregenerally prismatic-shaped, and preferably rectangular, with each casing126, 112 defining four linear or nonlinear sidewalls connected to a baseor central region, preferably planar. Alternatively, cathode casing 112can have a base with an area that protrudes outward from the peripheralpart of the casing base. At least one hole 118 is present in the bottomof cathode can 112 to act as an air entry port. The casings 112, 126,can include single or multiple steps if desired.

Referring to FIGS. 1 and 3, a catalytic positive electrode, such as airelectrode 20, 120 is disposed near the bottom of the cathode casing 12,112. As shown in greater detail in FIG. 1, the air electrode 120 caninclude a catalytic layer containing a mixture of carbon, anano-catalyst, and a binder. Air electrode 20, 120 also preferably has ahydrophobic layer 22, 122, such as a hydrophobic membrane or film,laminated thereon. The hydrophobic layer 22, 122 is laminated on theside of the air electrode closest to the bottom of the cell whenoriented as shown in FIGS. 1 and 2. Air electrode 20, 120 alsopreferably contains an electrically conductive current collector 123(FIG. 1), typically a metal screen or expanded metal, such as nickel ora nickel plated or clad iron or steel, embedded therein, preferably onthe side of the electrode opposite the hydrophobic layer 22, 122. Theair electrode may also optionally contain a barrier membrane 137, suchas a PTFE film, between the laminated hydrophobic layer 22, 122 and flatcentral region 14, 114 of the bottom of the casing 12, 112.

In a preferred embodiment, the catalytic layer 121 contains a catalyticcomposition that includes composite particles comprising nano-catalystparticles adhered to (e.g., adsorbed onto) the external and internalsurfaces (including surfaces of open pores) of highly porous carbonsubstrate particles.

The carbon material can be an activated carbon, preferably steamactivated carbon, and more preferably steam activated carbon derivedfrom coal. An activated carbon is a carbon with a specific surface area(BET method) of at least about 500 m²/g, with 1500 m² being achievable.Examples of steam activated carbons are Type PWA carbon (Calgon CarbonCorp., Pittsburgh, Pa., USA) and NORIT® Supra carbon, NORIT® Supercarbon and DARCO® G-60 carbon (all from American Norit Co., Inc.,Marshall, Tex., USA), with DARCO® G-60 carbon being a preferred steamactivated carbon. Typical properties of DARCO(® G-60 carbon include:carbon particles pass through a No. 100 sieve but do not pass through aNo. 325 sieve (US Standard Series sieves per ASTM E-11); a particle sizedistribution with a d₅₀ of about 34 μm, a d₅ of about 5.5 μm and a d₉₅of about 125 μm; a specific surface area (BET method) from about 600 toabout 1000 m²/g; a pore volume of about 0.95 ml/g, dry basis; a bulkdensity (tamped) of about 0.40 g/ml; and an iron content of the carbonno greater than 200 parts per million (ppm).

The nano-catalyst can be a metal, metal alloy or metal oxide withparticles of sub-micron size, at least one and preferably all of themetals of which can be selected from the transition metals (metalshaving incomplete d subshells) of groups 3-12, the metals of groups13-16, the lanthanides, mixtures, combinations and/or alloys thereof.Preferred metals include manganese, nickel, cobalt and silver, withmanganese being especially preferred. The nano-catalysts have primaryparticles with a maximum dimension of from about 1 nm to about 999 nm(0.999 em), referred to herein as nano-particles. As used herein,primary particles are particles that are bound together chemicallyrather than physically (e.g., by electrostatic charge, van der Waalsforces or moisture). Primary particles can form agglomerates of primaryparticles that are held together physically. Preferably the majority ofthe nano-catalyst particles are generally spherical with maximumdimensions of less than 50 nm, more preferably less than 20 nm, and mostpreferably less than 10 nm. The nano-catalyst can include oxidizednano-particles. The oxidized nano-particles can be fully or partiallyoxidized metal. A partially oxidized nano-particle can have a metal corewith an oxide shell. The oxide shell is preferably an essentiallycomplete shell, covering essentially the entire external surface of theparticle. Preferably at least the majority of the primary nano-particleshave at least an oxide shell (i.e., they are oxidized on at least theirexterior surfaces) to minimize agglomeration of the primary particlesand facilitate uniform mixing. More preferably at least 80 percent, andeven more preferably at least 90 percent, of the primary nano-particleshave at least an oxide shell. Most preferably no more than 5 percent ofthe nano-particles do not have at least an oxide shell. Nano-catalystsincluding oxidized nano-particles are available from QuantumSphere, Inc.(QSI), Santa Ana, Calif., USA.

A preferred nano-catalyst is a nano-manganese such as QSI-NANO®Manganese/Manganese Dioxide Powder, as disclosed in U.S. patentapplication Ser. No. 11/482,290, filed Jul. 6, 2006. In one embodiment,the nano-manganese can include a mixture of phases, such as metallicmanganese and one or more oxides of manganese, such as MnO, Mn₂O₃, andMn₃O₄. The overall composition of the nano-manganese can be MnO_(x),where x is from about 0.5 to about 2.0, preferably from about 0.7 toabout 1.3, and more preferably from about 0.9 to about 1.1. The primaryoxidized particles are generally sphere-like in shape, typically with amaximum dimension of about 20-30 nm in size, with some smallerparticles, down to 10 nm or less. The primary metallic manganeseparticles are generally rod-like in shape and typically about 20 nm inwidth and about 100 to 200 nm long. Primary particles can agglomerate toform larger clusters. It is generally desirable to minimizeagglomeration or break up agglomerates to achieve the most uniformdistribution of the nano-catalyst in the catalytic composition.

The catalytic composition can include a binder for binding the particlesof carbon together. The binder can be a fluorocarbon material, such aspolytetrafluoroethylene (PTFE). Suitable PTFE materials that can be usedto make the catalytic layer composition include TEFLON® materials(available from E.I. duPont de Nemours & Co., Polymer Products Div.,Wilmington, Del., USA), including powders such as TEFLON® 7C and,preferably, dispersions such as TEFLON® T30B, T30N, TE3857, TE3859 andmodifications thereof. More preferably the PTFE material is T30B or amodification of TE3859 (e.g., TE3859 fluorocarbon resin plus 2 percentTRITON™ X-100 octylphenol ethoxylate nonionic surfactant (Dow ChemicalCompany, Midland, Mich., USA) based on the weight of the TE3859). Thefluorocarbon binder can be fibrillated in the catalytic material mixingprocess.

In a preferred embodiment, the catalytic layer 121 of the electrode 120contains oxidized nano-manganese and activated carbon in a ratio of fromabout 0.01/1 to about 0.10/1 by weight and from 1-25 weight percent PTFEbinder (the minimum amount is more preferably at least 2, even morepreferably at least 5 and most preferably at least 7 weight percent; themaximum amount is more preferably no greater than 15 and most preferablyno greater than 12 weight percent).

The hydrophobic layer 22, 122 is hydrophobic material that has a lowenough surface tension to be resistant to wetting by the electrolyte,yet porous enough to allow the required gas (e.g., oxygen in the air fora metal-air cell) to enter the electrode at a rate sufficient to supportthe desired cell reaction rate. Fluorocarbon membranes such aspolytetrafluoroethylene (PTFE) can be used for the hydrophobic layer. Apreferred PTFE material is a high permeability material with an airpermeability value of from 1 to 300 seconds. A preferred PTFE materialhas an apparent density from about 1.5 to 1.7 g/cm². Examples ofpreferred materials are unsintered natural PTFE film, such as 0.10 mm(0.004 inch) thick PTFE membrane, product number N6389A (fromPerformance Plastics Product (3P), Houston, Tex., USA) with an airpermeability value of about 100-200 seconds and an apparent density ofabout 1.60±0.5 g/cm²; and expanded TEFLON® film, such as 0.076 mm (0.003inch) thick expanded film sample number 12850830.1 (from W.L. Gore &Associates, Inc., Elkton, Md., USA). The air permeability value is thetime required for 2.5 cm³ of air under a constant pressure of 30.94g/cm³ (12.2 inches of water, or 0.44 pounds/in²) to pass through an areaof 0.645 cm² (0.1 in²) and can be measured with a Gurley Densometer,Model 4150, for example.

At least one layer of separator 24, 124 is positioned on the side of theair electrode 20, 120 facing the anode 28, 128. The separator 24, 124 isionically conductive and electrically nonconductive. The total thicknessof the separator 24, 124 is preferably thin to minimize its volume, butmust be thick enough to prevent short circuits between the anode 28, 128and air electrode 20, 120. While there are advantages to a single layer,two (or more) layers may be needed to prevent short circuits through asingle pore, hole or tear in the material. For aqueous alkalinemetal-air cells, cellulosic materials such as rayon, cotton and woodfiber (e.g., paper) and combinations thereof are preferred. An exampleof a preferred separator is a combination of a layer of water-wettablenonwoven polypropylene membrane treated with surfactant (adjacent to theanode 28, 128) and a layer of hydrophobic polypropylene membrane(adjacent to the air electrode 20,120), such as CELGARD® 5550 andCELGARD® 3501 separators, respectively, both from Celgard, Inc.,Charlotte, N.C., USA. Another example of a preferred separator materialis rayon bound with polyacrylic acid (e.g., FS22824AB grade separatorfrom Carl Freudenberg KG, Weinheim, Germany, and BVA 02530 gradeseparator from Hollingsworth & Vose, East Walpole, Mass., USA). Theseparator 24, 124 is preferably adhered to the entire surface of the airelectrode 20, 120 to provide the best ion transport between theelectrodes and to prevent the formation of air pockets between the airelectrode 20, 120 and the separator 24, 124. Similarly, adjacent layersof the separator 24, 124 are adhered to each other.

A layer of porous material 138 can be positioned between air electrode20, 120 and the bottom of casing 12, 112 to evenly distribute air toelectrode 20, 120. A sealant 129 such as a thermoplastic hot meltadhesive, for example SWIFT® 82996 (from Forbo Adhesives, LLC ofResearch Triangle Park, N.C., USA) can be used to bond portions of thecathode to cathode casing 112.

Cell 10, 110 also includes anode casing 26, 126 which forms the top ofthe cell. The anode casing 126 in FIG. 1 has a rim 135 is flared outwardat its open end. The anode casing 26 in FIG. 3 has essentially straightside walls and that has a rim 35 with little or no outward flare.Alternatively, a cell can have a refold anode casing in which the rim isfolded outward and back along the side wall to form a substantiallyU-shaped side wall with a rounded edge at the open end of the casing.

The anode casing 26, 126 can be formed from a substrate including amaterial having a sufficient mechanical strength for the intended use.The anode casing 26, 126 can be a single layer of material such asstainless steel, mild steel, cold rolled steel, aluminum, titanium orcopper. Preferably the anode casing includes one or more additionallayers of material to provide good electrical contact to the exteriorsurface of the anode casing 26, 126, resistance of the external surfaceto corrosion, and resistance to internal cell gassing where the internalsurface of the anode casing 26, 126 comes in contact with the anode 28,128 or electrolyte. Each additional layer can be a metal such as nickel,tin, copper, or indium, or a combination or alloy thereof, and layerscan be of the same or different metals or alloys. Examples of platedsubstrates include nickel plated steel, nickel plated mild steel andnickel plated stainless steel. Examples of clad materials (i.e., laminarmaterials with at least one layer of metal bonded to another layer ofmetal) include, as listed in order from an outer layer to an innerlayer, two-layered (biclad) materials such as stainless steel/copper,three-layered (triclad) materials such as nickel/stainless steel/copperand nickel/mild steel/nickel, and materials with more than three cladlayers.

The anode casing 26, 126 can include a layer that is post-plated (i.e.,plated after forming the anode casing into its desired shape). Thepost-plated layer is preferably a layer of metal with a high hydrogenovervoltage to minimize hydrogen gassing within the cell 10, 110.Examples of such metals are copper, tin, zinc, indium and alloysthereof. A preferred metal is tin, and a preferred alloy is onecomprising copper, tin and zinc.

In one embodiment, illustrated in FIG. 2, the material of the anodecasing 126 in FIG. 1 has a substrate having a steel layer 144 pre-platedwith a layer of nickel 142 on each side, as well as a post-plated layer140 of tin or a copper-tin-zinc alloy for example. The anode casing 126in this embodiment can also be provided with a strike layer 146 betweenthe substrate and the post-plated layer 140. A preferred strike layer146 is a post-plated layer of copper which promotes adhesion between thesubstrate and the final post-plated layer 140.

In the embodiment shown in FIG. 3, anode casing 26 is made from anickel-stainless steel-copper triclad material, with the copper layer onthe inside, post-plated with tin or an alloy of copper, tin and zinc.The preferred composition of a layer of an alloy of copper, tin and zincincludes 50 to 70 weight percent copper, 26 to 42 weight percent tin,and 3 to 9 weight percent zinc. A strike layer of copper can bepost-plated onto the anode casing 26 prior to the final post-platedlayer to improve its adhesion to the triclad substrate material. Thecopper-tin-zinc alloy can be applied in multiple layers with the underlayer(s) having a higher copper content than the surface layer, asdescribed in detail in U.S. patent application Ser. No. 11/933,552,filed Nov. 1, 2007, which is hereby incorporated by reference.

The anode casing 26, 126 can be formed using any suitable process. Anexample is a stamping process. A button cell anode casing 26 ispreferably formed using three or more progressively sized stamping dies,after which the casing 26 is punched out of the coil of triclad strip.

During manufacture of the cell, anode casing 26, 126 can be inverted,and then a negative electrode composition or anode mixture 28, 128 andelectrolyte put into anode casing 26, 126. The anode mixture insertioncan be a two step process wherein dry anode mixture materials aredispensed first into the anode casing 26 followed by KOH solutiondispensing. In a prismatic cell, the wet and dry components of the anodemixture are preferably blended beforehand and then dispensed in one stepinto the anode casing 126. Electrolyte can creep or wick along the innersurface 36, 136 of the anode casing 26, 126, carrying with it materialscontained in anode mixture 28, 128 and/or the electrolyte.

An example of an anode mixture 28, for a button cell comprises a mixtureof zinc, electrolyte, and organic compounds. The anode mixture 28preferably includes zinc powder, a binder such as SANFRESH™ DK-500 MPS,CARBOPOL® 940 or CARBOPOL® 934, and a gassing inhibitor such as indiumhydroxide (In(OH)₃) in amounts of about 99.7 weight percent zinc, about0.25 weight percent binder, and about 0.045 weight percent indiumhydroxide. SANFRESH™ DK-500 MPS is a crosslinked sodium polyacrylatefrom Tomen America Inc. of New York, N.Y., and CARBOPOL® 934 andCARBOPOL® 940 are acrylic acid polymers in the 100% acid form and areavailable from Noveon Inc. of Cleveland, Ohio.

The electrolyte composition for a button cell can be a mixture of about97 weight percent potassium hydroxide (KOH) solution where the potassiumhydroxide solution is 28-40 weight percent, preferably 30-35 weightpercent, and more preferably about 33 weight percent aqueous KOHsolution, about 3.00 weight percent zinc oxide (ZnO), and a very smallamount of CARBOWAX® 550, which is a polyethylene glycol based compoundavailable from Union Carbide Corp., preferably in an amount of about 10to 500 ppm, more preferably about 30 to 100 ppm, based on the weight ofzinc composition in the anode.

An anode mixture 128, for a prismatic cell can include a mixture ofzinc, electrolyte, and organic compounds. The anode mixture 128preferably includes zinc powder, electrolyte solution, a binder such asCARBOPOL® 940, and gassing inhibitor(s) such as indium hydroxide(In(OH)₃) and DISPERBYK® D190 in amounts of about 60 to about 80 weightpercent zinc, about 20 to about 40 weight percent electrolyte solution,about 0.25 to about 0.50 weight percent binder, about 0.045 weightpercent indium hydroxide and a small amount of DISPERBYK® D190,preferably in an amount of about 10 to 500 ppm, more preferably about100 ppm, based on the weight of zinc. DISPERBYK® D190 is an anionicpolymer and is available from Byk Chemie of Wallingford, Conn.

The electrolyte composition for a prismatic cell can be a mixture ofabout 97 weight percent potassium hydroxide (KOH) solution where thepotassium hydroxide solution is about 28 to about 40 weight percent,preferably about 30 to about 35 weight percent, and more preferablyabout 33 weight percent aqueous KOH solution, and about 1.00 weightpercent zinc oxide (ZnO).

Preferred zinc powders are low-gassing zinc compositions suitable foruse in alkaline cells with no added mercury. Examples are disclosed inU.S. Pat. No. 6,602,629 (Guo et al.), U.S. Pat. No. 5,464,709 (Getz etal.) and U.S. Pat. No. 5,312,476 (Uemura et al.), which are herebyincorporated by reference.

One example of a low-gassing zinc is ZCA grade 1230 zinc powder fromZinc Corporation of America, Monaca, Pa., USA, which is a zinc alloycontaining about 400 to about 550 parts per million (ppm) of lead. Thezinc powder preferably contains a maximum of 1.5 (more preferably amaximum of 0.5) weight percent zinc oxide (ZnO). Furthermore, the zincpowder may have certain impurities. The impurities of chromium, iron,molybdenum, arsenic, antimony, and vanadium preferably total 25 ppmmaximum based on the weight of zinc. Also, the impurities of chromium,iron, molybdenum, arsenic, antimony, vanadium, cadmium, copper, nickel,tin, and aluminum preferably total no more than 68 ppm of the zincpowder composition by weight. More preferably, the zinc powder containsno more than the following amounts of iron, cadmium, copper, tin,chromium, nickel, molybdenum, arsenic, vanadium, aluminum, andgermanium, based on/the weight of zinc: Fe-3.5 ppm, Cd-8 ppm, Cu-8 ppm,Sn-5 ppm, Cr-3 ppm, Ni-6 ppm, Mo-0.25 ppm, As-0.1 ppm, Sb-0.25 ppm, V-2ppm, Al-3 ppm, and Ge-0.06 ppm.

In another embodiment, the zinc powder preferably is a zinc alloycomposition containing bismuth, indium and aluminum. The zinc alloypreferably contains about 100 ppm of bismuth, 200 ppm of indium, and 100ppm of aluminum. The zinc alloy preferably contains a low level of lead,such as about 35 ppm or less. In a preferred embodiment, the averageparticle size (D₅₀) is about 90 to about 120 microns. Examples ofsuitable zinc alloys include product grades NGBIA 100, NGBIA 115, andBIA available from N.V. Umicore, S.A., Brussels, Belgium.

Cell 10, 110 also includes a gasket 30, 130 made from an elastomericmaterial which serves as the seal. The bottom edge of the gasket 30, 130has been formed to create an inwardly facing lip 32, 132, which abutsthe rim of anode casing 26, 126. Optionally, a sealant may be applied tothe sealing surface of the gasket, cathode casing and/or anode casing.Suitable sealant materials will be recognized by one skilled in the art.Examples include asphalt, either alone or with elastomeric materials orethylene vinyl acetate, aliphatic or fatty polyamides, and thermoplasticelastomers such as polyolefins, polyamine, polyethylene, polypropyleneand polyisobutene. A preferred sealant is SWIFT® 82996, describedhereinabove.

The cathode casing 12, 112, including the inserted air electrode 20, 120and associated membranes can be inverted and pressed against the anodecup/gasket assembly, which can be preassembled with the casing invertedso the rim of the casing faces upward. While inverted, the edge of thecathode casing 12, 112 can be deformed inwardly, so the rim 34, 134 ofthe cathode casing 12, 112 is compressed against the elastomeric gasket30, 130, which is between the cathode casing 12, 112 and the anodecasing 26, 126, thereby forming a seal and an electrical barrier betweenthe anode casing 26, 126 and the cathode casing 12, 112.

Any suitable method may be used to deform the edge of the casing inwardto seal the cell, including crimping, colleting, swaging, redrawing, andcombinations thereof as appropriate. Preferably the button cell issealed by crimping or colleting with a segmented die so that the cellcan be easily removed from the die while a better seal is produced. Asused herein, a segmented die is a die whose forming surfaces comprisesegments that may be spread apart to enlarge the opening into/from whichthe cell being closed is inserted and removed. Preferably portions ofthe segments are joined or held together so they are not free floating,in order to prevent individual segments from moving independently andeither damaging the cell or interfering with its insertion or removal.Preferred crimping mechanisms and processes are disclosed in commonlyowned U.S. Pat. No. 6,256,853, which is hereby incorporated byreference. Preferably a prismatic cell is sealed by crimping.

A suitable tab (not shown) can be placed over the opening 18, 118 untilthe cell 10, 110 is ready for use to keep air from entering the cell 10,110 before use.

A catalytic composition for the active layer of a catalytic electrodecan be made from a catalytic mix using a nano-catalyst or precursor toprovide a composite catalytic material containing at least partiallyoxidized nano-catalyst particles adhered to the external surfaces andthe internal surfaces (the surfaces of the pores) of the carbonparticles. Oxidation of the nano-catalyst particles or formation ofoxidized nano-catalyst particles from a precursor can take place beforeor during the mixing process. The degree of oxidation can be controlled.The oxide can provide one or more functions, such as aiding thecatalytic reaction, imparting stability, and/or reducing agglomerationof the nano-particles.

In a process in which the nano-catalyst is oxidized during mixing of thecatalytic mix ingredients, nano-metal particles are at least partiallyoxidized after being adhered to carbon particles by separately mixingboth the nano-metal particles with a liquid medium, preferably adeoxygenated liquid medium such as a deoxygenated lower alcohol, mixingtogether the nano-metal and carbon mixtures, and then partiallyoxidizing the nano-metal particles by bringing the nano-particles intocontact with an oxidant after the nano-metal particles are adhered tothe carbon particle surfaces. A binder, such as a fluorocarbon material,can be used to adhere the nano-metal particles to the carbon. Thedeoxygenated liquid medium can be removed prior to adding the oxidant,or an oxidant can be added before removing the liquid medium. To preventnon-controlled oxidation of the nano-metal before adding the oxidant,the mixing steps prior to addition of the oxidant can be carried out inan environment in which oxidation of the nano-metal is substantiallyprevented, such as in an inert gas (e.g., argon) atmosphere. Anysuitable oxidant can be used, such as O₂, O₃, nitrogen oxides (e.g.,N_(x)O_(y), where x=1−2 and y−1−5), and halogen oxides. In someembodiments water can be used as an oxidant. Mixtures of oxidants canalso be used.

The nano-catalyst can be formed from a precursor, such as by thereduction of potassium permanganate dissolved in a liquid medium, toform particles of the insoluble nano-catalyst (manganese oxide) on theinternal and external surfaces of the carbon particles. In oneembodiment, a catalytic composition for an active layer of an electrodecan be made as follows; the quantities are representative and quantitiesand proportions can be varied. About 400 g to 1500 g distilled water isplaced into a large beaker with a volume of about 3 times the watervolume. About ⅓ the water weight of activated carbon (e.g., DARCO® G-60from American Norit Corp. or equivalent) is added to the water.Potassium permanganate (KMnO₄) in an amount up to about the weight ofthe carbon (e.g., about ⅓ the weight of the carbon) is added to themixture slowly while stirring, resulting in up to about 15% by weight asmanganese (Mn) in the final dry catalytic composition. The KMnO₄ can beadded as dry crystals or as a prepared solution of about 20% KMnO₄ inwater. The above components are mixed for sufficient time (e.g., atleast 20 minutes) for the activated carbon to reduce the KMnO₄ in situto Mn(+2); water can be added if the mixture is too viscous to be easilystirred. From about 0.07 g to about 0.44 g of PTFE dispersion (TEFLON®30b from E.I. DuPont de Nemours & Co., Polymer Products Division) pergram of carbon can be added while stirring the mixture to provide a dryPTFE content of from about 3 weight percent to about 25 weight percentof the total mixture; electrodes comprising up to about 50 weightpercent PTFE are useful in some applications. The mixture is furthermixed, e.g., for at least about 30 minutes, to insure that all of thePTFE particles to attach themselves to the carbon particles. The mixtureis then filtered to remove a substantial portion of the liquid andtransferred to a non-corrosive pan, preferably with a thickness of thedamp mix of not more than about 5.1 cm (2 inches), dried in a preheatedventilation oven at 75° C. for at least 24 hours, then further dried ina preheated oven at 120° C. for 12 hours in an open container to producedried Teflonated carbon. The Teflonated carbon is covered, cooled tobelow 100° C. and then sealed in a plastic bag. Nano-catalyst materialis added to the Teflonated carbon (from about 0.01 to about 20 weightpercent nano-catalyst in the resultant catalytic composition). Thecatalytic composition can be blended in a very high sheer blender forfrom about 30 seconds to about 5 minutes.

In another embodiment, a catalytic composition can be made as follows;the quantities are representative and quantities and proportions can bevaried. Distilled water (500 g) is placed into a large beaker, to whichactivated carbon powder (e.g., 15 g of DARCO® G-60 or equivalent) isslowly added, mixing slowly to dampen the carbon. Using a mixer such asa propeller type mixer, the water and carbon are stirred sufficiently tocreate a stable vortex while mixing for about 20 minutes, withoutdrawing air into the mixture (i.e., without the vortex touching theblade). Slowly (over about 30 seconds) about 250 g of 20% KMnO₄ solutionis added to the stirring mixture, and then mixing is continued for about30 minutes more. Very slowly (over about 1 minute), 25 cc of PTFEdispersion (TEFLON® 30b) is added while stirring, and stirring iscontinued for 30 minutes more, while maintaining the stable vortex andnot drawing air into the mixture. When the PTFE dispersion is added, themixture initially becomes very viscous, then less so as the PTFEparticles become adhered to the carbon particles. The mixture is thenfiltered to remove a substantial portion of the liquid and transferredto a non-corrosive pan, dried in a preheated ventilation oven at 75° C.for 24 hours, then further dried in a preheated oven at 120° C. for 12hours to produce dried Teflonated carbon. The Teflonated carbon iscovered, cooled to below 100° C. and then sealed in a plastic bag.Nano-catalyst material is added to the Teflonated carbon (e.g., about 10weight percent nano-catalyst in the resultant catalytic composition).The catalytic composition can be blended in a very high sheer blenderfor from about 30 seconds to about 5 minutes.

In yet another embodiment, a catalytic composition can be made asfollows; the quantities are representative and quantities andproportions can be varied. Distilled water (about 500 g) is placed intoa large beaker, and activated carbon powder (150 grams of DARCO® G-60 orequivalent) is added, mixing slowly to dampen the carbon. Using a mixersuch as a propeller type mixer, the water and carbon are stirredsufficiently to create a stable vortex while mixing for about 20minutes, without drawing air into the mixture (i.e., without the vortextouching the blade). Very slowly (over about 1 minute), 25 cc of PTFEdispersion (TEFLON® 30b) is added while stirring, and stirring iscontinued for 30 minutes more, while maintaining the stable vortex andnot drawing air into the mixture. When the PTFE dispersion is added, themixture initially becomes very viscous, then less so as the PTFEparticles become adhered to the carbon particles. The mixture is thenfiltered and transferred to a non-corrosive pan, dried in a preheatedventilation oven at 110° C. for 24 hours to produce dried Teflonatedcarbon. The Teflonated carbon is covered, cooled to below 100° C. andsealed in a plastic bag that is stored in an inert atmosphere (e.g., ina chamber filled with nitrogen and/or argon gas). In an inertatmosphere, a nano-catalyst (preferably nano-manganese or nano-manganesealloy particles that are at least partially oxidized) are mixed withabout 3 times their weight of deoxygenated methanol (MeOH) to form anink (e.g., a black, substantially opaque liquid), the ink is optionallymixed ultrasonically, and the ink is then sealed in a vial. A mixture of1 part of the dried Teflonated carbon and 4 parts MeOH was preparedunder an inert atmosphere. Under an inert atmosphere, nano-catalyst inkis mixed with Teflonated carbon for at least 2 minutes; the quantitiesof ink and carbon are typically selected to provide from about 5 weightpercent to about 15 weight percent nano-catalyst on a dry basis. The inkand carbon mixture is removed from the inert atmosphere after standingfor about 15 minutes to allow the nano-catalyst to adsorb into thecarbon particles to coat the pores (i.e., the internal surfaces of thecarbon). The ink and carbon mixture is dried by placing it in aventilated oven pre-heated to 105° C. until the mixture reaches 105° C.(e.g., for about 100 minutes for 5 g of the mixture); the nano-catalystcan be oxidized in situ (e.g., nano-manganese is oxidized tocatalytically active MnO_(x) in this drying step. The dried catalyticcomposition can be covered and cooled to room temperature.

A catalytic composition for the active layer of a catalytic electrodecan be made, at least partially oxidizing the nano-catalyst metal insitu, according to the following steps:

-   1. Add distilled water to activated carbon, cover and allow the    carbon to wet up.-   2. Thoroughly mix the carbon and water with a high intensity,    variable speed mixer, adjusting the mixer speed to produce a vortex    that extends about half way to but does not reach the bottom of the    container.-   3. While continuing the mixing, add PTFE dispersion dropwise to the    vortex, adjusting the mixer speed to maintain the desired vortex,    and continue mixing until the mixer reaches about the same speed as    prior to adding the PTFE dispersion.-   4. Filter the water from the mixture, rinsing with distilled water.-   5. Dry the remaining carbon mix at 90° C. until the mix reaches 90°    C., increase the drying temperature to 105° C. and continue drying    until the mix reaches 105° C., continue drying at 105° C. for    several more hours, and reduce the temperature to 50° C. and    continue drying until the mix reaches 50° C.; place the dry carbon    mix in a sealed container while hot and allow to cool to room    temperature.-   6. In an argon atmosphere, mix each of the carbon mix and    nano-catalyst (with or without at least partially oxidized    particles) with deoxygenated methanol separately, mix the two    together, add a small amount of distilled water, and mix well; cover    and remove from the argon atmosphere.-   7. Dry the carbon-catalyst mixture at 90° C. until the mix reaches    90° C., increase the drying temperature to 105° C. and continue    drying until the mix reaches 105° C., continue drying at 105° C. for    several hours more, reduce the temperature to 50° C. and continue    drying until the mix reaches 50° C.; place the mix in a sealed    container and allow to cool to room temperature.

The catalytic composition can also be prepared using nano-catalystparticles that have been partially oxidized before mixing with otheringredients of the catalytic composition. In some embodiments this caneliminate the need to perform mixing operations in an inert environmentas well as the need to use a liquid such as deoxygenated alcohol.Accordingly, in one embodiment the liquid medium contains no more than20 weight percent alcohol, preferably no more than 10 weight percentalcohol and more preferably no more than 5 weight percent alcohol; mostpreferably the liquid medium is essentially alcohol-free.

In an embodiment of the invention, the catalytic composition for theactive layer of the catalytic electrode is made according to thefollowing steps:

-   1. Add distilled water to activated carbon, cover and allow the    carbon to wet up.-   2. Thoroughly mix the carbon and water with a high intensity,    variable speed mixer, adjusting the mixer speed to produce a vortex    that extends about half way to but does not reach the bottom of the    container.-   3. While continuing the mixing, slowly add nano-catalyst (with at    least partially oxidized particles); continue to mix thoroughly,    adjusting the mixer speed as necessary to maintain the desired    vortex.-   4. Add PTFE dispersion dropwise to the vortex; continue to mix,    adjusting the mixer speed as necessary to maintain the desired    vortex, until the mixer reaches about the same speed as prior to    adding the PTFE dispersion.-   5. Filter the water from the catalytic mix, rinsing with distilled    water and filter again.-   6. Dry at 90° C. until the mix reaches 90° C.; increase the drying    temperature to 105° C. and continue drying until the mix reaches    105° C.; continue drying at 105° C. for several more hours; reduce    the temperature to 50° C. and continue drying until the mix    temperature reaches 50° C.; place the mix in a sealed container and    allow to cool to room temperature.

In another embodiment, larger batches of catalytic composition can bemade in an air environment without dangerous solvents using commerciallyavailable mixers. Examples of mixers that can be used include an IKA®Universulmühle M20 Mix Mill (IKA North America, Wilmington, N.C., USA),and a PK® blender (Patterson-Kelly, Stroudsburg, Pa., USA). Thecatalytic mix can be made according to the following steps:

-   1. Weigh the desired quantities of nano-catalyst (with at least    partially oxidized particles), activated carbon, PTFE dispersion    (mix the PTFE dispersion well before weighing), and water    (optional).-   2. Load the activated carbon and nano-catalyst into the mixer and    blend thoroughly.-   3. Add the PTFE dispersion and mix thoroughly.-   4. Dry the catalytic mix. This can be done in a drying mixer, such    as an FM50 PLOUGHSHARE® horizontal mixer from Littleford Day, Inc.    (Forence, Ky., USA) set at 381 mm (15 inches) vacuum, a plow blade    speed of 180 revolutions per minute (RPM), a chopper blade speed of    3000 (RPM) cycling 20 seconds per minute and a temperature of about    74 to 85° C. (165 to 185° F.), for a total of about 94 minutes.    Drying the mix in a mixer can advantageously keep the mix in    constant motion and fibrillate the PTFE during drying.

In an embodiment of the invention, the catalytic mix is milled to form asheet of catalytic material that is used as the catalytic layer of thecatalytic electrode according to the following steps:

-   1. Mix the dried catalytic mix in a high sheer blender to fluff the    mix.-   2. Feed the fluffed mix between the rollers of a roller mill    (preferably from the top) operating at a speed that will produce    about 1.5 meters (5 feet) per minute of catalytic sheet at the    desired thickness.

In an embodiment of the invention, a catalytic electrode is madeaccording to the following steps:

-   1. Embed a piece of current collector into a surface of the    catalytic sheet. This can be done, for example, by pressing between    two flat plates or, preferably between the rollers of a roller mill.    When using a roller mill, feed the current collector and catalytic    sheet between the rollers (preferably horizontally, with the current    collector on the bottom, to facilitate feeding), preferably with the    roller mill operating at a speed of about 1.5 meters (5 feet) per    minute to embed the current collector into the catalytic sheet. It    is desirable to embed the current collector to a sufficient depth to    provide a relatively smooth surface on the electrode in order to get    the desired adhesion of the separator layer to the electrode.-   2. Trim the catalytic sheet and/or current collector as desired.-   3. Pressure laminate a corresponding sheet of hydrophobic film to    the catalytic sheet using a roller mill, preferably on the side    opposite that of the current collector. Preferably the hydrophobic    film and catalytic sheet are feed into the roller mill horizontally,    with the hydrophobic film on top. Optionally, the bond strength    between the hydrophobic layer and the catalytic layer can be    increased, such as by one or both of the following:    -   a. Spray one surface of the hydrophobic film with a dilute        fluorocarbon resin emulsion, such as 10 weight percent T30 PTFE        dispersion in water, allow to dry, and then pressure laminate        the hydrophobic film to the catalytic layer; and    -   b. Pattern laminate the hydrophobic film to the catalytic layer        to create areas of increased bond strength while leaving areas        therebetween in which any reductions in air permeability of the        hydrophobic film and the catalytic layer are minimized.        Preferred methods of pattern-laminating the hydrophobic film to        the catalytic layer include using a textured roller against the        hydrophobic film and using a removable textured interleaf        material (e.g., a woven material with high strength threads,        such as silk) between the hydrophobic film and the adjacent        roller. When using a textured roller, a fine pattern with very        thin (e.g., 0.03 to 0.1 mm) raised portions with small areas        (e.g., 0.15 to 0.25 mm across) located therebetween. An example        of a suitable silk material is one having a thickness of about        0.16 mm (0.006 inch) and a thread count of about 100 per 2.54 cm        (1.0 inch) in each direction, with each thread containing about        50 strands of silk.

In an embodiment of the invention, the surface of the current collectoris treated to minimize the internal resistance of the electrode. Apreferred current collector material, particularly for small cells suchas button cells, is an expanded nickel (e.g., nickel EXMET™ from DexmetCorp., Naugatuck, Conn., USA), preferably one with a base metalthickness from 0.05 to 0.127 and more preferably from 0.06 to 0.08 mm.The expanded nickel material is preferably equivalent to a 40 mesh (40openings per inch) screen. Another preferred current collector material,particularly for cells larger than button cells, is a woven wire clothwith cross-bonded wires (wires welded where they cross), preferably 40to 50 mesh (40 to 50 openings per inch) with a wire diameter of 0.10 to0.15 mm (available from Gerard Daniel Worldwide, Fontana, Calif., USA).The surface of the current collector can be treated by acid etching,such as with nitric acid, to roughen the metal surfaces. Alternatively,the current collector can be coated with a carbon containing material,such as a graphite coating. Examples of suitable graphite coatingmaterials include: TIMREX® LB1000, LB1016 and LB1090 aqueous graphitedispersions (TIMCAL America, Westlake, Ohio, USA), ECCOCOAT® 257 (W. R.Grace & Co.), and ELECTRODAG® 109 and 112 and EB0005 (AchesonIndustries, Port Huron, Mich., USA).

In an embodiment of the invention, the density of the catalytic sheetprior to lamination of the hydrophobic sheet is about 8 to 20 mg/cm²,preferably 9 to 13 mg/cm². If the density is too high, the thickness ofthe final electrode can be too great, and if the density is too low, theelectrode may have insufficient strength.

In an embodiment of the invention, the bond strength between thehydrophobic layer and the catalytic layer of the electrode is preferablyat least 65, more preferably at least 75 and most preferably at least 85g per 25.4 mm (1 inch), as determined by a peel strength test. Tomaintain sufficient permeability and prevent damage to the airelectrode, the bond strength is preferably no greater than 250, and morepreferably no greater than 200 g per 25.4 mm (1 inch). The peel strengthtest measures the force required to peel the hydrophobic layer away fromthe air electrode and is done using a Chatillon Model TCD200 tester,fitted with 25.4 mm (1 inch) wide serrated jaw clamps. The tester isprogrammed with a bottom stop, at which the clamps are about 8.5 mm (⅓inch) apart, and a top stop that allows the clamps to separate to about50.8 mm (2 inches). The top clamp is brought to the bottom stop positionand the force gauge is zeroed. A sample piece of electrode about 38.1 mm(1.5 inches) long is cut, and the hydrophobic membrane is peeled backevenly by a small amount (no more than 12.7 mm (½ inch)) from a cutedge. The exposed catalytic layer is clamped to the bottom clamp and theloose end of the hydrophobic membrane is clamped to the top clamp, withthe sample centered and square. The top clamp is raised, recording theinitial high gauge reading. The peel strength is calculated as theinitial high gauge reading per unit width of the sample.

In an embodiment of the invention, the catalytic electrode, includingthe catalytic layer, current collector and hydrophobic layer, has athickness from about 0.15 to 0.35 mm, preferably from 0.19 to 0.25 mm,and more preferably from 0.19 to 0.21 mm. If the electrode is too thick,it will occupy excessive volume within the cell. If it is too thin, itmay be weak, leading to distortion or damage. Preferably the variationin thickness will be no greater than 0.03 mm and more preferably nogreater than 0.015 mm. If the variation is too great, manufacturingproblems such as cell assembly problems, damage, camber and scrap canresult due to dimensional variation of the sheet. For cell designs suchas those shown in FIGS. 1 and 3, excessive thickness variation can alsocontribute to increased electrolyte leakage. Areas of high and lowpressure can be also be created during electrode manufacturing, leadingto areas of high and low permeability of the laminated electrode andareas of high and low bond strength of the hydrophobic layer to thecatalytic layer, thereby adversely affecting cell performance andresistance to leakage.

In an embodiment of the invention, one or more layers of separator areadhered to the surface of the catalytic electrode opposite thehydrophobic layer. This can be done using an adhesive applied to one orboth of the adjacent surfaces of the electrode and the separator andadjacent surfaces of layers of separator. A preferred adhesive containsa polyvinyl alcohol (PVA), more preferably PVA thickened withcarboxymethylcellulose (CMC) or polyacrylic acetate (PAA). Preferablythe PVA adhesive contains as little PVA as possible. An example of apreferred PVA adhesive is one prepared by slowly adding about 7 weightpercent PVA (e.g., PVA 52-22) to cold water while mixing with a highsheer mixer, slowly heating to 95° C. while continuing to mix, slowlyadding about 1.4 weight percent CMC while continuing to mix, mixinguntil the solution is dissolved to clarity, sealing the solution in asterile glass container, and allowing to cool to room temperature.

In an embodiment of the invention, a sheet of separator is adhered tothe electrode and, when there is a second separator layer, a secondsheet of separator is adhered to the first by painting a thin layer ofadhesive on the electrode or layer of separator on the electrode anddrying at 80° C., painting a thin layer of adhesive onto the sheet ofseparator to be adhered, applying the adhesive-painted separator sheetto the electrode or separator-laminated electrode, and drying.

In an embodiment of the invention, a sheet of separator is pressurelaminated to the catalytic electrode, using, for example, a roller mill.Preferably the separator is laminated to the catalytic layer withembedded current collector before laminating the hydrophobic layer toavoid damage to the hydrophobic layer, since higher pressure may berequired for separator lamination. For a 2-layer separator, the secondlayer is adhered to the layer adjacent the catalytic layer of theelectrode using an adhesive. This can be done after pressure laminatingthe first separator layer to the electrode, or, preferably, the twoseparator layers can be laminated together with an adhesive, followed bypressure lamination of the two-layer separator to the electrode.

In an embodiment of the invention, the catalytic electrode is capable ofproviding a maximum power from 220 mW/cm² to 700 mW/cm² on a Half-CellPotential Dynamic Scan test as described below. Preferably the maximumpower is at least 250 mW/cm², more preferably at least 275 mW/cm².

EXAMPLE 1

A conventional air electrode for an alkaline zinc-air cell was made. Theelectrode had a catalytic layer containing 70 weight percent carbon(Calgon PWA), 25 weight percent PTFE with surfactant (from TE30B), and 5weight percent MnO_(x). The catalytic layer was formed with a thicknessof about 0.203 mm (0.008 inch) and a packing of about 38 percent(percentage of maximum theoretical density based on the theoreticaldensities of the component materials). An expanded nickel currentcollector (4Ni5-060 P&L 0.127 mm (0.005 inch) thick nickel EXMET™ fromDexmet), painted with an aqueous graphite dispersion (50 weight percentTIMREX® LB1016 in water)) was embedded under 684 kg (1508 pounds) forceinto the catalytic layer, with a final thickness of about 0.279 mm(0.011 inch). A sheet of 0.076 mm (0.003 inch) thick expanded PTFEmembrane (Sample No. 12850830.1 from W.L. Gore) was pressure laminatedto the surface of the catalytic layer opposite the surface into whichthe current collector was embedded to produce a laminated air electrodesheet.

EXAMPLE 2

A nano-catalyst air electrode was made with nano-MnO_(x) according tothe following steps:

-   1. 300 g DARCO® G-60 carbon was placed in a 2000 ml glass container,    1000 g distilled water was added, and the container was covered and    allowed to sit for one hour.-   2. The mixture was mixed for about 30 minutes with an adjustable    speed mixer, adjusting the speed to maintain a vortex extending    about half way to the bottom of the container.-   3. 55 g T30B PTFE was added dropwise while mixing, and mixing was    continued for about 20 minutes, adjusting the speed to maintain the    desired vortex.-   4. The mixture was filtered, while rinsing with about 200 ml    distilled water.-   5. The remaining solids (the mix) were dried at about 85-90° C. for    about 16 hours, then the temperature was increased to 105° C. and    drying continued until the temperature of the mix reached 105° C.;    then the mix was covered and allowed to cool to room temperature.-   6. In an argon gas atmosphere, 10 grams of the mix was put into a    porcelain bowl and mixed with 50 grams deoxygenated methanol.-   7. In argon, 0.256 g nano-MnO_(x) (QSI-NANO® Manganese) was mixed    with 3 grams deoxygenated methanol.-   8. In argon, the carbon/methanol and nano-MnO_(x)/methanol mixtures    were mixed together for about 30 seconds, about 10 ml distilled    water was mixed in, and the mixture covered and removed from the    argon atmosphere.-   9. The mix from step 8 was put at 105° C. until the mix temperature    reached 105° C., then covered and allowed to cool to room    temperature.-   10. The mix was blended in a high sheer blender for 30 seconds and    then fed between the rollers of a roller mill, set to 0 clearance    and operating at a rate of 1.37 m (4.5 feet) per minute, to form a    sheet of catalytic material 0.18 mm thick, with a density of 0.213    mg/cm³ and containing 2.50 weight percent nano-manganese.-   11. The catalytic sheet was placed on top of a strip of current    collector (3Ni3.3-05P nickel EXMET™, painted with an aqueous    graphite dispersion (50 weight percent TIMREX® LB1016 in water)),    and both were fed horizontally between the rolls of a roller mill,    operating at a rate of 1.37 m (4.5 feet) per minute and applying 684    kg (1508 pounds) force, to embed the current collector into the    catalytic sheet and form a sheet with a thickness of 0.248 mm    (0.00975 inch).-   12. A sheet of 0.076 mm (0.003 inch) thick expanded PTFE membrane    (Sample No. 12850830.1 from W.L. Gore) was placed on top of the    catalytic sheet with embedded current collector, and a sheet of 100    mesh (100 threads per inch) silk cloth was placed over the PTFE    membrane. All three were fed horizontally between the rolls of a    roller mill operating at a rate of 1.37 m (4.5 feet) per minute and    applying 684 kg (1508 pounds) force to pressure laminate the PTFE    membrane to the catalytic layer, thereby forming an air electrode    stock.

EXAMPLE 3

A sheet of BVA 02530 separator (Hollingsworth & Vose) was glued to theelectrode sheets from each of Examples 1 and 2, on the surfaces of theair electrodes opposite the PTFE membranes, using pressure and a PVA/CMCadhesive. Sample electrodes were cut from each of the sheets andassembled into PR44 size alkaline zinc-air button cells.

Cells with electrodes from each of Examples 1 and 2 were tested for opencircuit voltage, followed by AC impedance, with a peak to peak potentialamplitude of 10 mV, over a frequency range from 65 KHz to 0.1 Hz. Thiswas followed by a potential dynamic scan in the cathodic direction,beginning at 0.025 V above the open circuit voltage and scanning at 1mV/sec. to 0.7 V. This initial AC impedance and potential dynamic scantesting served to condition the catalytic electrodes. After 30 minutesopen circuit, the AC impedance and potential dynamic scan tests wererepeated, and these results were used. From the potential dynamicvoltage scan, a voltammogram (Tafel curve) and a polarization curve wereplotted. The Tafel curve is shown in FIG. 4, where the observed current(amps/cell) is on the x-axis using a log scale, and applied potential(volts) is on the y-axis. The results of the AC impedance and potentialdynamic voltage scan testing are summarized in Table 1.

TABLE 1 Parameter Units Example 1 Example 2 CCV at 4 mA volts 1.2941.298 CCV at 10 mA volts 1.221 1.255 Power at 1.0 V mW 27.2 72.8 SteadyState R of iR ohms 9.52 5.27 10 KHz Capacitance μF 39.5 125 1 KHzCapacitance μF 491 1527 65 KHz Impedance ohms 0.554 0.510 10 KHzImpedance ohms 0.731 0.489 1 KHz Impedance ohms 1.310 0.612

Cells were also discharged at 100 ohms continuous. The closed circuitvoltage of cells with electrodes from Example 2 was about 40 mV higherthan that of cells with electrodes from Example 1.

EXAMPLE 4

A nano-catalyst air electrode was made with nano-MnO_(x) according tothe following steps:

-   1. 200 g DARCO® G-60 carbon was placed in a 1500 ml glass container,    900 g distilled water was added, and the container was covered and    allowed to sit for about 15 minutes.-   2. The mixture was mixed for about 15 minutes with an adjustable    speed mixer, adjusting the speed to maintain a vortex extending    about half way to the bottom of the container.-   3. Mixing was continued while 5.6 g nano-MnO_(x) (QSI-NANO®    Manganese) was slowly (over about 30 seconds) added to the vortex    and the sides of the container were rinsed with deionized water,    followed by about 15 minutes of additional mixing, adjusting the    mixer speed to maintain the desired vortex.-   4. Mixing was continued while 26 g of T30B PTFE was added dropwise    to the vortex, followed by about 20 minutes of additional mixing,    adjusting the mixer speed to maintain the desired vortex.-   5. The mixture was filtered, while rinsing with about 500 ml    distilled water.-   6. The remaining solids (the mix) were dried at 90° C. until the mix    temperature reached 90° C., the temperature was increased to 105° C.    and drying continued until the temperature of the mix reached 105°    C., drying at 105° C. was continued for about another 4-6 hours, and    the drying temperature was reduced to 50° C.; then the mix was    sealed in a container and allowed to cool to room temperature.-   7. The dried mix was fluidized by blending in a high speed mixer (5    g for 30 seconds or 50 g for 5 minutes), and then fed between the    rollers of a roller mill, set to 0 clearance and operating at a rate    of 1.52 m (5 feet) per minute, to form a sheet of catalytic material    0.19 mm thick, with a density of 0.212 mg/cm³ and containing 2.50    weight percent nano-manganese.-   8. The catalytic sheet was placed on top of a strip of current    collector (3Ni3.3-05P nickel EXMET™, and both were fed horizontally    between the rolls of a roller mill, operating at a rate of 1.52 m (5    feet) per minute, to embed the current collector into the catalytic    sheet and form a sheet with a thickness of 0.19 mm (0.0075 inch).-   9. A sheet of 0.076 mm (0.003 inch) thick expanded PTFE membrane    (Sample No. 12850830.1 from W.L. Gore) was placed on top of the    catalytic sheet with embedded current collector, a sheet of 100 mesh    silk cloth was placed over the PTFE membrane, and all three were fed    horizontally between the rolls of a roller mill operating at a rate    of 1.52 m (5 feet) per minute to pressure laminate the PTFE membrane    to the catalytic layer, thereby forming an air electrode stock.

EXAMPLE 5

An air electrode was made following the same steps in Example 4, exceptthat step 3 was skipped, so no catalyst was added to the carbon mixtureand only the activated carbon was present as a catalytic material.

EXAMPLE 6

Electrodes from each of Examples 4 and 5 were tested in half cellfixture with a platinum counter electrode and a zinc reference electrodeand flooded with 33 weight percent KOH. For each electrode the opencircuit voltage was tested, followed by AC impedance, with a peak topeak potential amplitude of 10 mV, over a frequency range in thecathodic direction, beginning at 0.025 V above the open circuit voltageand scanning at 1 mV/sec. to 0.7 V vs. the reference electrode. Thisinitial AC impedance and potential dynamic scan testing served tocondition the catalytic electrodes. After 30 minutes open circuit, theAC impedance and potential dynamic scan tests were repeated, and theseresults were used. This test is referred to herein as the Half Cell ACImpedance/Dynamic Potential Scan Test. From the dynamic potential scandata, a polarization curve (similar to a Tafel curve, but with a linearrather than log scale for current density) was plotted. The results ofthe AC impedance and potential dynamic scan tests are summarized inTable 2.

TABLE 2 Parameter Units Example 4 Example 5 CCV at 10 mA volts 1.3631.311 CCV at 100 mA volts 1.342 1.225 Maximum Power mW/cm² 527 327 Powerat 1.0 V mW 400 273 Current Density @ 1.1 V mA/cm² 268 188 CurrentDensity @ 1.0 V mA/cm² 400 273 Limiting Current mA/cm² 652 523 SteadyState R of iR ohms 1.52 1.06 65 KHz Impedance ohms 0.66 0.60 65 KHzCapacitance μF 5.87 7.12 10 KHz Capacitance μF 190 216 1 KHz CapacitanceμF 8393 8842

EXAMPLE 7

An air electrode sheet was made with conventional MnO_(x) catalyst asdescribed in Example 1, except that the hydrophobic membrane was a 0.10mm (0.004 inch) thick CD123 PTFE film from 3P, and the current collectorwas made from 3Ni3.3-05P nickel EXMET™. Two layers of separator(CELGARD® 3501 adjacent to the electrode sheet and CELGARD® 5550) werelaminated to the surface of the electrode sheet opposite the hydrophobiclayer using a PVA adhesive. Individual electrodes were cut from thesheet and assembled into PR44 size alkaline zinc-air button cells.

EXAMPLE 8

An air electrode sheet was made with nano-MnO_(x) as described inExample 2, but with a 3Ni3.3-05P nickel EXMET™ current collector. Twolayers of separator were laminated to the surface of the electrode sheetas in Example 7. Individual electrodes were cut from the sheet andassembled into PR44 size alkaline zinc-air button cells.

EXAMPLE 9

Cells from each of Examples 7 and 8 were tested as described in Example3. The polarization curve is shown in FIG. 6.

EXAMPLE 10

Sheets of air electrodes made as described in Example 4 using two typesof current collector materials (4Ni5-060 P&L nickel EXMET™ from Dexmetand cross-bonded 40 mesh (40 openings per inch) nickel screen with 0.15mm (0.006 inch) diameter wires from Gerard Daniel Worldwide, Fontana,Calif., USA). Some were painted with an aqueous graphite dispersion (50weight percent TIMREX® LB1016 in water) as shown in Table 3. Electrodeswere cut from each sheet and tested on an AC impedance test, at opencircuit potential, with a peak to peak potential amplitude of 10 mV,over a frequency range from 100 KHz to 0.1 Hz. The average ohmicresistance (Re), charge transfer (Rct) and double layer capacitance(Cdl) for each are shown in Table 3.

TABLE 3 Current Collector Re (ohms) Rct (ohms) Cdl (μF) EXMET ™ uncoated1.06 0.03 2568 EXMET ™ coated 0.64 0.07 2660 Screen coated 0.71 0.071337

EXAMPLE 11

Two nano-catalyst mixes were made with nano-MnO_(x) as described inExample 4 except for the amounts of activated carbon, nano-catalyst andbinder used. The quantities used and the compositions of the catalyticlayers of the resultant dried electrodes are summarized in Table 4. Twocatalytic electrodes were made with each of the mixes as described inExample 4 except the material used for the current collectors was4Ni5-060 EXMET™, the current collectors were coated with TIMREX® LB1016graphite dispersion as described in Example 10, and a silk clothinterleaf material was not used in laminating the PTFE membrane to thecatalytic sheet for one of the electrodes made with each mix.

TABLE 4 Mix A Mix B Mix Ingredients (grams) Activated Carbon 205.8 205.9Nano-Manganese 5.3 7.1 PTFE Dispersion 26.5 118.4 Dry Composition (wt %)Activated Carbon 90.5 72.5 Nano-Manganese 2.5 2.5 PTFE 7.0 25.0

Each of the four lots of electrodes made was tested on the Half Cell ACImpedance/Potential Scan Test described in Example 6. Results of thepotential dynamic scan portion of the test are summarized in Table 5.

TABLE 5 Mix A Mix B No Silk No Silk Parameter Units Interleaf InterleafInterleaf Interleaf CCV at 10 mA volts 1.380 1.380 1.359 1.377 CCV at100 mA volts 1.202 1.265 1.178 1.258 Maximum Power mW/cm² 202 318 134288

All references cited herein are expressly incorporated herein byreference in their entireties. To the extent publications and patents orpatent applications incorporated by reference contradict the disclosurecontained in the present specification, the present specification isintended to supersede and/or take precedence over any such contradictorymaterial.

It will be understood by those who practice the invention and thoseskilled in the art that various modifications and improvements may bemade to the invention without departing from the spirit of the disclosedconcept. The scope of protection afforded is to be determined by theclaims and by the breadth of interpretation allowed by law.

1. An electrochemical cell comprising a catalytic electrode, a counterelectrode, a separator between the catalytic and counter electrodes, andan electrolyte, all disposed within a housing having at least oneopening for allowing a gas to enter into or escape from the housing;wherein: the catalytic electrode has a multilayer structure comprisingan active layer and a gas diffusion layer; the active layer comprises acatalytic material for oxidizing or reducing an active material, anelectrically conductive material, and a binder; the gas diffusion layercomprises a material that is permeable to the gas entering or escapingthe housing and is essentially impermeable to the electrolyte to sealthe electrolyte within the housing; and the gas diffusion layer has asurface with a gas diffusion area for diffusion of the gas therethrough,the entire gas diffusion area is adhered to the active layer, andadhesion of the gas diffusion area to the active layer has areas ofrelatively high adhesion and areas of relatively low adhesion.
 2. Thecell according to claim 1, wherein the adhesion of the gas diffusionarea to the active layer is characterized by an overall bond strength offrom 65 to 250 grams per 25.4 mm and the catalytic electrode hassufficient permeability to be capable of providing 220 mW/cm² to 700mW/cm² maximum power on a Half Cell AC Impedance/Potential Dynamic Scantest.
 3. The cell according to claim 2, wherein the bond strength is atleast 75 grams per 25.4 mm and the maximum power the catalytic electrodeis capable of providing on the Half Cell AC Impedance/Potential DynamicScan test is at least 250 mW/cm².
 4. The cell according to claim 1,wherein the gas diffusion layer is pressure bonded to the active layer.5. The cell according to claim 1, wherein the gas diffusion layermaterial is a fluorinated polymer.
 6. The cell according to claim 5,wherein the gas diffusion layer sheet comprises apolytetrafluoroethylene sheet.
 7. The cell according to claim 6, whereinthe polytetrafluoroethylene sheet, prior to bonding the gas diffusionlayer sheet to the active layer sheet, has an air permeability value offrom 1 to 300 seconds and an apparent density of 1.5 to 1.7 g/cm². 8.The cell according to claim 1, wherein the electrolyte is an aqueousalkaline electrolyte and the gas diffusion layer material is ahydrophobic material.
 9. The cell according to claim 8, wherein thecounter electrode comprises zinc as an active material.
 10. The cellaccording to claim 9, wherein the cell contains no added mercury. 11.The cell according to claim 1, wherein the catalytic electrode is anoxygen reduction material capable of reducing oxygen entering thehousing through the one or more openings therein.
 12. The cell accordingto claim 1, wherein the catalytic material comprises a manganese oxiderepresented by an overall formula MnO_(x), where x is from 0.5 to 2.0.13. The cell according to claim 1, wherein the catalytic materialcomprises a composite material comprising nano-metal particles adheredto activated carbon particles.
 14. The cell according to claim 13,wherein the nano-metal particles comprise nano-manganese.
 15. Anelectrochemical cell comprising a catalytic electrode, a counterelectrode, a separator between the catalytic and counter electrodes, andan aqueous alkaline electrolyte, all disposed within a housing having atleast one opening for allowing oxygen to enter the housing; wherein: thecatalytic electrode has a multilayer structure comprising an activelayer, a gas diffusion layer and a current collector; the active layercomprises a catalytic material, an electrically conductive carbon and abinder; the gas diffusion layer comprises a polytetrafluoroethylenematerial that is permeable to the oxygen entering the housing and isessentially impermeable to the electrolyte to seal the electrolytewithin the housing; the gas diffusion layer has a surface with a gasdiffusion area for diffusion of the oxygen therethrough to the activelayer, the entire gas diffusion area is adhered to the active layer, andadhesion of the gas diffusion area to the active layer has areas ofrelatively high adhesion and areas of relatively low adhesion; bondstrength of from 65 grams per 25.4 mm to 250 grams per 25.4 mm; thecatalytic electrode has sufficient permeability to be capable ofproviding 220 mW/cm² to 700 mW/cm² maximum power on a Half Cell ACImpedance/Potential Dynamic Scan test; the current collector comprisesan expanded metal comprising nickel, coated with graphite; and the cellcontains no added mercury.
 16. A process for making a catalyticelectrode for an electrochemical cell, comprising the steps: (a) mixinga catalytic material for oxidizing or reducing an active material withan electrically conductive material and a binder; (b) forming themixture from step (a) into an active layer sheet; (c) disposing a firstsurface of a gas diffusion layer sheet against a first surface of theactive layer sheet; (d) applying pressure to a second surface of theactive layer sheet and a second surface of the gas diffusion layer sheetto bond the gas diffusion layer sheet to the active layer sheet toproduce a gas diffusion area for diffusion of a gas therethrough to theactive area such that the entire gas diffusion area is bonded to theactive layer with areas of relatively high adhesion and relatively lowadhesion between the gas diffusion layer and active layer; and (e)forming the bonded layers into an electrode having adhesion betweenessentially the entire adjacent second surfaces of the bonded layers.17. The process according to claim 16, wherein a first surface of atextured interleaf sheet is disposed against the second surface of thegas diffusion layer sheet, and the pressure is applied to the secondsurfaces of the interleaf sheet and the gas diffusion layer sheet. 18.The process according to claim 17, wherein the textured interleaf sheetcomprises woven threads, fibers, filaments, hairs, or wires.
 19. Theprocess according to claim 18, wherein the interleaf sheet comprises awoven silk fabric.
 20. The process according to claim 17, wherein thepressure is applied by a combination of two plates, platens or rollers.21. The process according to claim 16, wherein the adhesion of the gasdiffusion area to the active layer is characterized by an overall bondstrength of from 65 grams per 25.4 mm to 250 grams per 25.4 mm and thecatalytic.
 22. The process according to claim 16, wherein the pressureis applied by a combination of two plates, platens or rollers, at leastone of which has a textured surface to produce the areas of relativelyhigh adhesion and relatively low adhesion.
 23. The process according toclaim 16, wherein the gas diffusion layer sheet comprises a hydrophobicmaterial.
 24. The process according to claim 23, wherein the hydrophobicmaterial comprises a fluorinated polymer.
 25. The process according toclaim 24, wherein the gas diffusion layer sheet comprises apolytetrafluoroethylene sheet.
 26. The process according to claim 25,wherein the polytetrafluoroethylene sheet, prior to bonding the gasdiffusion layer sheet to the active layer sheet, has an air permeabilityvalue of from 1 to 300 seconds and an apparent density of 1.5 to 1.7g/cm².
 27. The process according to claim 16, wherein the processfurther comprises the step of incorporating an electrically conductivecurrent collector.
 28. The process according to claim 27, wherein thecurrent collector is made from an expanded metal comprising nickel andhas a coating comprising graphite.
 29. The process according to claim27, wherein the current collector is embedded into the second surface ofthe active layer sheet.